Current Drive VS Voltsge Drive

[GlennGregor]

I would like to know if anyone has info on Current Drive systems for audio. I have a Current Drive Integrated Amplifier and the sound is amazing. I run a pair of Yamaha S5115HT’s off of it and the music is flawless. These are my house speakers. Their sensitivity is 100. I don’t know if a Current Drive system would work as well with low sensitivity speakers. I’d really like to get some feedback on this.

 

[Lambda]

Most try to keep the resistance of speaker wires as low as possible... a current drive is basically the opposite.
Its like punting an big( infinite) resistor in series.

 

[GlennGregor]

Most try to keep the resistance of speaker wires as low as possible... a current drive is basically the opposite.
Its like punting a big( infinite) resistor in series.

Current Drive seems superior to Voltage Drive, but why does it seem that not many people seem to know anything about it. Even the internet doesn’t have allot of info on Current Drive for audio.

 

[DonH56]

It's been discussed here a little; a search might turn up some posts but I am not sure there's a thread devoted to it. There's a book about it, linked below, but my take is the author is pretty biased toward current drive and glosses over a lot of the practical problems with it. One common (IME) counter argument is that crossovers are typically designed to be driven from a voltage source (ideally 0-ohm driving impedance) and thus will not produce the designer's target frequency response with a high-impedance (current-drive) input. Current drive will also allow interaction among drivers and potentially uncontrolled voltage from any charge kickback produced by the electromechanical motor/generator action in the drivers. I have not seen any real evidence that current drive is superior (not that I've done an exhaustive search or series of experiments; my reading and measurements are pretty limited) and for better or worse virtually all speakers today assume a voltage source driving them.

Amazon.com

Some of the "current drive" amplifiers in the past were not true current amps and/or used voltage feedback so as a black box tended to look like a voltage source when operating normally.

 

[EdW]

Current Drive seems superior to Voltage Drive, but why does it seem that not many people seem to know anything about it. Even the internet doesn’t have allot of info on Current Drive for audio.

It’s also possible that the phrase “Current Drive” used in the description of the amplifier is a phrase that the marketing dept liked the sound of and doesn’t have a great deal of similarity with what the engineers realised when they designed and built the amplifier . .

 

[GlennGregor]

It's been discussed here a little; a search might turn up some posts but I am not sure there's a thread devoted to it. There's a book about it, linked below, but my take is the author is pretty biased toward current drive and glosses over a lot of the practical problems with it. One common (IME) counter argument is that crossovers are typically designed to be driven from a voltage source (ideally 0-ohm driving impedance) and thus will not produce the designer's target frequency response with a high-impedance (current-drive) input. Current drive will also allow interaction among drivers and potentially uncontrolled voltage from any charge kickback produced by the electromechanical motor/generator action in the drivers. I have not seen any real evidence that current drive is superior (not that I've done an exhaustive search or series of experiments; my reading and measurements are pretty limited) and for better or worse virtually all speakers today assume a voltage source driving them.

Amazon.com

Some of the "current drive" amplifiers in the past were not true current amps and/or used voltage feedback so as a black box tended to look like a voltage source when operating normally.

I have a Sony TA-F555ES integrated amplifier made in 1983. It’s a true Current Drive. Sony called it “Audio Current Transfer”. So it seems that the big problem with Current Drive is finding the right speakers to match it to.

 

[EdW]

I have a Sony TA-F555ES integrated amplifier made in 1983. It’s a true Current Drive. Sony called it “Audio Current Transfer”. So it seems that the big problem with Current Drive is finding the right speakers to match it to.

Audio current transfer refers to the interface between the preamp and power amp

Sony TA-F555ES on thevintageknob.org

vintage Sony ES 1980s audiophile amplifier with Audio Current Transfer

www.thevintageknob.org

So not the drive to the speakers

 

[voodooless]

Audio current transfer refers to the interface between the preamp and power amp

Sony TA-F555ES on thevintageknob.org

vintage Sony ES 1980s audiophile amplifier with Audio Current Transfer

www.thevintageknob.org

So not the drive to the speakers

So it’s not at all a current drive amp at all . Karma?

 

[EdW]

So it’s not at all a current drive amp at all . Karma?

Right first time! Although driving a loudspeaker with a current dependent on the audio level would sound pretty strange with loudspeaker impedances varying perhaps 20:1 over the band

 

[oleg87]

Current Drive seems superior to Voltage Drive, but why does it seem that not many people seem to know anything about it. Even the internet doesn’t have allot of info on Current Drive for audio.

How does it "seem" superior? There's no conspiracy against it, it creates more problems than it solves.

 

[EdW]

I would like to know if anyone has info on Current Drive systems for audio. I have a Current Drive Integrated Amplifier and the sound is amazing. I run a pair of Yamaha S5115HT’s off of it and the music is flawless. These are my house speakers. Their sensitivity is 100. I don’t know if a Current Drive system would work as well with low sensitivity speakers. I’d really like to get some feedback on this.

Replying to your original quest now that the issue of the current drive is understood this amp seems pretty good

Sony TA-F555ES Integrated Amplifier Review price specs - Hi-Fi Classic

www.hifi-classic.net

Watch out for speaker impedance though - it doesn’t like low impedance speakers. Make sure the speaker doesn’t go below 4 ohms

EDIT correct link

 

[DonH56]

I have a Sony TA-F555ES integrated amplifier made in 1983. It’s a true Current Drive. Sony called it “Audio Current Transfer”. So it seems that the big problem with Current Drive is finding the right speakers to match it to.

Not quite as noted above by @EdW -- the description is about the signal link from internal preamp to amplifier stages.

"Inaugurated here was ACT (Audio Current Transfer) which uses current amplification to transfer signals from preamp to power amp stage and achieve 120dB of dynamic range and outstanding levels of stereo separation."

You can do that with voltage, of course, and many have, but in fact current-mode signal routing is something I have done for many years in the high-speed analog world. It has its pros and cons, of course. Since much signal coupling occurs as voltage-mode signals via parasitic capacitance, an argument can be made for using current-mode signals so there is no (or very little) voltage swing on interconnects. That does have some advantages in certain applications and often offers greater noise immunity (again, in some but not all cases, depends upon the type of noise and coupling mechanism). Without voltage swing, crosstalk among channels can be reduced, assuming inductive coupling is well controlled/reduced (not too hard for audio; can get a bit more challenging at RF/mW frequencies). There are real-world problems no matter what you do.

 

[Sokel]

So it’s not at all a current drive amp at all . Karma?

Like this one?

Eclipse mono : HALCRO

The world's only Super-Fidelity amplifiers

halcro.com

What's the benefits of such an input?

Edit: @DonH56 already answered.

 

[McFly]

I know little of the subject, but I thought for a true current drive amplifier to work, the connected impedance had to be ruler flat, or the output of the amplifier be specifically designed to drive one speaker or driver only? Making current drive amplifiers kind of practically useless in the real world?

 

[GlennGregor]

How does it "seem" superior? There's no conspiracy against it, it creates more problems than it solves.

There is no loopback from the speskers, so the problem with the EMF is eliminated. That’s just one thing. Headroom is phenomenal. I can play any song and it sounds fabulous, whether it’s AC/DC, Roberta Flack, Neil Diamond, or Led Zeppelin. No need for HiRes recordings because .MP3’s sound superb. These are just some of the benefits of a Current Drive.

 

[JSmith]

Current Drive seems superior to Voltage Drive

A thorough article on this subject, with further references;

Current Drive

ESP Project Pages - High Output Impedance aka current drive. Does it make a difference?

sound-au.com

JSmith

 

[DonH56]

I know little of the subject, but I thought for a true current drive amplifier to work, the connected impedance had to be ruler flat, or the output of the amplifier be specifically designed to drive one speaker or driver only? Making current drive amplifiers kind of practically useless in the real world?

No, it depends upon the load characteristics. A voice coil is basically an inductor with a magnetic field generated by the current through it (or voltage across it). That magnetic field, determined by the applied signal from your amplifier, modulates the static magnetic field of the permanent magnet inside the voice coil, causing the speaker's cone to move forward and back in response to the signal (music or whatever). The pro current-drive crowd says that, since the voice coil is basically an inductor with magnetic field created by the current through it, why not just drive it directly with a current? The counters are that (1) it is not a pure inductance, especially with the crossover (and parasitic elements) considered, and (2) whether you generate the current by sending a current directly to the coil, or by applying a voltage across the coil that creates the same current, the end result is the same -- music.

It is common to speak of current amplifiers driving into a flat, often near-zero ohm, load to reduce voltage swings but you can design the load to be driven by current or voltage. Just need to ensure the transfer function from input (current or voltage) to output (sound) is linear and meets the frequency response target.

 

[DonH56]

There is no loopback from the speskers, so the problem with the EMF is eliminated. That’s just one thing. Headroom is phenomenal. I can play any song and it sounds fabulous, whether it’s AC/DC, Roberta Flack, Neil Diamond, or Led Zeppelin. No need for HiRes recordings because .MP3’s sound superb. These are just some of the benefits of a Current Drive.

The amplifier you linked does not provide current drive to the speakers, just the low-level signal inside from preamp stage to amplifier stage. I think the output (driving the speakers) is a conventional class AB amplifier. Which by no means detracts from its great sound! Just not current drive to the speakers.

MP3 offers a wide variety of compression levels.

@restorer-john -- Do you know what the Sony TA-F555ES output stage is like? My memory of these Sony units is pretty vague at this point, despite having seen and even owned a few back then.

 

[Prana Ferox]

You can just say "I'm dumping 100 wpc of clean power into big-a** horns in my house, and it sounds great" and of course we're going to assume that's correct

 

[restorer-john]

There is no loopback from the speskers, so the problem with the EMF is eliminated. That’s just one thing. Headroom is phenomenal. I can play any song and it sounds fabulous, whether it’s AC/DC, Roberta Flack, Neil Diamond, or Led Zeppelin. No need for HiRes recordings because .MP3’s sound superb. These are just some of the benefits of a Current Drive.

ACT (Audio Current Transfer) was used in several Sony integrateds (and some sources like tuners) in the 1980s. It was short lived. The amplifiers were pretty good, although rather ugly with the volume control on the 'wrong' side.

The power stage is realtively conventional, and I really am not a fan of tone controls in the negative feedback loop.

The block diagram:

I've got a TA-F444es (1986) in the storeroom. It was comprehensively bettered by the TA-F333esR from 1989.

They really weren't pretty on the inside either:

Single pair LAPT (diffused emitters) Sanken MT200s per channel.